Particles of different sizes and shapes (i.e. different materials) can become suspended in air for any of several different reasons. Tiny, condensed water droplets or ice crystals that become suspended in the atmosphere as clouds are a good example of this phenomenon. Clouds of particles, other than water, that may become suspended in air, such as dust and smoke, are also well known examples of the phenomenon. Unfortunately, smoke can be generated with many types of materials that will most likely cause undesirable consequences. In any event, and particularly in the case of smoke, it may be desirable or necessary to identify the type(s) of particles that constitute the smoke cloud.
Physically, it is well known that different types of particles, when suspended in air as a cloud, will affect light differently. In particular, it is known that particles in a cloud will scatter the light that is incident on the cloud and, depending on the nature of the particles in the cloud, the incident light will be scattered in a predictable and detectable manner. Importantly, the measurable characteristics of the scattered light depend on at least three significant factors. For one, if the incident light is polarized, when it is incident on particles in a cloud the light may change its polarization. If so, the polarization of the scattered light will be different from that of the incident light. For another, the wavelength (λ) of the incident light that interacts with the particles in the cloud will determine the extent of scattering. Further, detection of the scattered light will be influenced by where the detector is located relative to the beam path of the incident light (i.e. a scattering angle (θ)). In summary, the detection of a signal that is generated when light is scattered by a smoke cloud is dependent on the polarization of the incident light, the wavelength (λ) of the incident light, and the scattering angle (θ) where the detector happens to be located.
For purposes of the present invention, the above factors are important because different smoke and dust particles will scatter a same incident light beam differently. Further, it can be shown that relatively benign particles, though detectably different, have characteristically similar responses. Accordingly, as a group, they can be differentiated from the group of responses that are characteristically different and are typical of potentially hazardous or toxic particles (e.g. petrochemicals).
In light of the above, it is an object of the present invention to provide an optical unit for a smoke analyzer system that evaluates signals received from light scattered by a smoke cloud to determine whether the smoke includes particularly hazardous or toxic materials. Another object of the present invention is to provide an optical unit for a smoke analyzer system that generates signals for evaluation, wherein the signals are based on polarization, wavelength and scattering angle considerations. Yet another object of the present invention is to provide an optical unit for a smoke analyzer that is easy to use, is simple to manufacture and is comparatively cost effective.